Serotonin (5-HT) is known to play a major role both in Central Nervous System (CNS) and in Peripheral Nervous System (PNS). Compounds acting as 5-HT receptor antagonists may be effectively used in the prevention or treatment of migraine, cluster headaches and trigeminal neuralgia. They may also be used in the treatment of certain CNS disorders such as anxiety and psychosis. Since 5-HT antagonists may have a beneficial role on gastrointestinal motility a further use of these compounds is in the treatment of delayed gastric emptying, and related disorders such as dyspepsia, flatulence, oesophageal reflux, peptic ulcer, constipation and irritable bowel syndrome. Very recently it has been also discovered that a number of 5-HT antagonists may be particularly useful in the treatment of chemotherapy induced nausea and emesis (J. R. Fozard-Trends in Pharmacological Sciences 8 44, 1987, and references cited therein).